The invention is directed to rotary, longitudinally extendable and retractable soot blower lances for cleaning interior surfaces of high temperature boilers, such as used in power generation, for example, particularly for use in areas of boilers that are exposed to high levels of radiant heat.
In the operation of large fossil fuel boilers, especially coal boilers, accumulations of slag and soot form on the walls and on the tube structures on the inside of the boilers, tending gradually to reduce the efficiency of heat transfer within the boiler system. To minimize the effect of these slag and soot accumulations, large boilers typically are provided with a plurality of appropriately located soot blower units. These soot blower units can be of a rotary retracting type, each including an elongated, rotary tubular lance provided at its outer end with nozzles or the discharge of water or, more typically, steam or air.
During the soot blowing operation, as the lance is projected into and then retracted from the interior of the boiler, it is of course subjected to the extremely high temperatures prevailing within the boiler. In those areas of the boiler in which the lance is exposed directly to the flame, it is subjected to not only the convection heat of the hot gases but also (and more significantly) radiant heat from the fire area. As a result, the operating life of a soot blower lance exposed to radiant heat tends to be relatively short. The life of the lance may be extended in some measure by forcing through the lance excess amounts of the cleaning fluid, in order to provide a degree of additional cooling for the exposed lance. While this is somewhat helpful in extending the life of the lance, it of course involves offsetting expenses from the excess consumption of steam, air or other cooling medium.
In accordance with the present invention, the operating life of certain types of lances, namely lances constructed in the first instance of high temperature steels and intended for use in radiant heat areas of a boiler (hereinafter referred to as "high temperature lances"), can be significantly extended by producing a thin coating of ceramic material about the exterior surface of the lance. A relatively thin coating of such ceramic material greatly reduces the rate of heat absorption of the lance material, especially the absorption of radiation heat, which is the most significant source of heat input to the lance.
High temperature steam lances utilizing the principals of the invention can be operated with up to 15-30% less steam flow, while at the same time enjoying a significantly increased operating life.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention and to the accompanying drawing.